I am very interested but it's not clear to me whether these are minus
alpha releases or something intented for production...

I would say kfreebsd-i386 is roughly "unstable" as other ports
are in "unstable". kfreebsd-amd64 is younger port and is slightly worse.
Current status would be beta for kfreebsd-i386 and late alpha or
early beta for kfreebsd-amd64.
The easiest way is to evaluate is to just try, i.e. inside qemu.
Petr